Detection of chemical species using solid state sensors is of great practical importance. The niche for chemical microsensors exists in places where continuous measurement of a chemical concentration is required from a number of locations. Microsensors require small volume of chemical and have low power requirements. The integration of electrochemically active thin films with conventional IC process enables integrated circuit chemical microsensors which have advantages of the small size and robustness of solid-state devices. Addition of real-time monitoring along with these attributes, make them particularly attractive for bio-medical applications.
A 'PCB packaged' chemical sensor using standard CMOS technology has been developed for pH measurements. The standard CMOS process is attractive for developing the sensor because of ready availability of on-chip circuitry for analog and digital signal processing. The single post-processing step leads to the formation of the active sensing area on the chip. Simplicity of the post-processing step can be gauged by the fact that only crude photolithography is required in obtaining the active area which consists of aluminium oxide film. Bulk micromachining is also a maskless step leading to a probe type of a sensors.
Although micro-sensors for measuring physical parameters like acceleration, position, temperature and light are commercially successful, such developments are yet forthcoming in the field of chemical sensors. The approach given in this thesis can lead to commercial possibilities of chemical sensor due to low fabrication costs, high reliability of the CMOS process and short turn around times. The device developed can also be used as a test vehicle for exploring novel films (like gallium nitride) as an alternative for active area deposition. This can be done by depositing different active area films instead of aluminium oxide.
August 30, 1995
Jani, D. B. (1995). CMOS Based Chemical Sensors. (n.p.): University of California, Los Angeles.